Okay, let's break this down and analyze whether a NEMA 1 or NEMA 12 JOA selector switch likely falls under the exception regarding listing for intrinsically safe applications, based on the information provided.

Understanding the Context Intrinsically Safe (IS) Apparatus

This refers to equipment designed to not cause ignition of flammable or explosive atmospheres. IS systems limit the energy available in a circuit to levels below what's needed to cause ignition.

Associated Apparatus

This is equipment that's not necessarily intrinsically safe itself but is used in conjunction with intrinsically safe apparatus. It usually provides power or signals to the IS apparatus but is designed and installed so that it doesn't compromise the safety of the IS system.

Listing

Equipment is "listed" when an independent testing laboratory (like UL, CSA, FM) has evaluated it and found it to meet certain safety standards. This is a crucial requirement for IS apparatus.

Simple Apparatus

This is the key to your question. The exception says that simple apparatus doesn't need to be listed, provided it's described on the control drawing.

Control Drawing

This is a critical document that defines the intrinsically safe system, including the allowed parameters for all components, wiring, and installation requirements.

Analysis of NEMA-1 and NEMA-12 Selector Switches as JOAJOA (Junction Operating Assembly)A selector switch on a JOA is most likely not a simple apparatus if it has any electronics attached to it.-A simple selector switch with no electronics can be considered a simple apparatus.

The Crucial Factor: "Simple Apparatus"

The definition of "simple apparatus" is critical. Per the exception, it needs to be described on the control drawing.

Typical Simple Apparatus



Resistors

Passive components with known and stable resistance values.

Simple Switches

Mechanical switches that simply open or close a circuit. They should not contain any internal electronics (e.g., transistors, integrated circuits, power supplies).

Junction Boxes

Enclosures for making wiring connections.

Cable

simple wire

Why the Exception Exists

The "simple apparatus" exception exists because these devices, by their nature, don't introduce significant energy into a circuit and are unlikely to cause ignition.

Therefore

If the JOA selector switch in question is a truly simple mechanical switch (just contacts opening and closing), then it may be permissible to omit the listing if it is listed on the control drawing.

Important Considerations



Consult the Control Drawing

The control drawing is the definitive source. If the selector switch is described on the drawing and meets the definition of "simple apparatus" as defined in the standards and by the certifying body of the equipment, it may be acceptable to use a non-listed switch.

Authority Having Jurisdiction (AHJ)

The AHJ (e.g., the electrical inspector) has the final say. They can overrule anything, so it's best to discuss any questions with them beforehand.

Risk Assessment

Even if the code allows it, perform a thorough risk assessment.

Disclaimer: I am an AI chatbot and cannot provide definitive legal or engineering advice. This information is for educational purposes only. Always consult with qualified professionals for specific applications. Flag for review